Energy Myths- Fact or Fiction?

MYTH: Closing off vents and registers will reduce your heating bill.
False. If you have a modern forced air heating system, the pressure load is balanced throughout the house. Blocking the vent will impact how the system inhales and exhales air; it can throw the system out of balance, causing it to have to work harder or possibly break down.

Also the most energy efficient practice you can do is to have heat evenly distributed throughout the house. Blocking vents in certain rooms will make those rooms colder. Because heat moves from greater concentrations to lesser concentrations, these colder rooms will draw heat from other rooms in the house, making the whole house feel colder and causing you to raise the thermostat.

MYTH:  Fiberglas insulation alone keeps cold air out of your home.
Fiberglas actually does a better job at keeping heat in than keeping cold out. If you have cracks, air leaks and drafts anywhere in your house, the cold air will seep in no matter how much insulation you have. Air sealing is the most important thing you can do to plug these holes and gaps and keep the chill from creeping in.

MYTH:  Leaving a ceiling fan on will cool a room…even when you’re not there.
Fans cool your skin, not the air; they do not lower room temperature. A fan works by circulating the air in a space; when the air moves across the skin, we feel cooler even though the air temperature in the room remains the same. If a fan runs in a room when no one is there, no one is feeling its benefits. So it’s just wasting electricity.

MYTH: Buying an energy efficient furnace or air-conditioner will automatically reduce my energy bill.
Not necessarily true. Even the highest efficiency-rated heaters and air conditioners can cost you more money to operate if they are improperly sized or installed.  According to the Department of Energy, shoddy installation and improper sized equipment can waste as much as one-third of your energy consumption.

MYTH: Duct tape is good for sealing ducts.
Duct tapes has many great uses. But despite the name, it actually does a pretty lousy job at sealing ducts.  It doesn’t work well in dirty or dusty conditions…and you can’t get dirtier or dustier than an air duct. Also, the tape tends to fall off as it ages and the adhesive dries out. Mastic tape sticks, seals and insulates much better.

MYTH: The higher you set your thermostat, the faster your furnace will heat up your house.
False. Furnaces deliver heat at the same rate no matter how high the thermostat is set. If you set your thermostat at the desired temperature, it will reach that point just as quickly as if you set it higher. And since you’ll probably end up having to move the temperature down a few degrees anyway, you’ll probably wind up using more energy than you intended in the long run.

The same applies to air conditioning. Setting your A/C at full-blast will not make it reach a comfortable temperature any faster. It’s just going to make the room colder and make your system work harder.

MYTH:  There’s no benefit in adjusting your thermostat when you don’t need heating or cooling…such as at night or when nobody’s home.
Research shows that the longer your house stays at a reduced temperature when heating or at an increased temperature when cooling, the more energy and money you will save. This is because heating and cooling cost depends mostly on the difference between indoor and outdoor temperature. When you adjust the temperature down in the winter or up in the summer, you simply reduce this temperature difference. In fact, setting your temperature back 10 or more degrees for 8 hours while you sleep or go to work can reduce your energy bill by 5-15%.  A programmable thermostat can adjust temperatures automatically for you.

MYTH:  Leaving lights, computers and appliances on uses less energy than turning them off and on repeatedly.
This may have been true of computers 20 or more years ago when they were massive energy hogs and prone to energy surge damage and wear & tear. But today’s computers are much more durable and use a lot less energy. The small surge in energy created when any electrical product is turned on is much smaller than the energy used by running the device when it’s not needed. Rule of thumb: any time you can turn a machine or light off, it will save energy.

MYTH: It requires less energy to boil water if you fill your pot with hot water from the tap.
Totally bogus. It takes the same amount of energy to reach the boiling point whether you use hot or cold water. If you use hot water, you’ve already paid to heat the water in your water heater; you may have a headstart of a few degrees, but you’ve already paid for that headstart.

MYTH: A dripping faucet is not all that significant.
Really? Put a bucket underneath and see how quickly those drips add up. A single dripping faucet can add up to 300 or more gallons of water per month. That’s a big chunk of your water bill.

MYTH: Showering uses less energy and water than taking a bath. 
This one is true! Taking a 10-minute shower with a low-flow (2.5 gallons per minute) shower head uses 25 gallons of water. A typical bath takes 30-50 gallons. There are high-quality hower heads that use 1.5 gallons per minute or less for even more water and energy efficiency.

MYTH: Energy efficiency increases the initial cost of a home.
Not necessarily. There is little if any correlation between energy efficiency and a home’s purchase price. In some instances, efficiency can even reduce the initial cost when smaller highly-efficient heating and cooling systems are installed. Smaller, high efficiency units generate as much heating or cooling benefits as large, inefficient ones.

MYTH: Energy efficiency doesn’t appeal to home buyers and doesn’t enhance a home’s future sales price of the home.
Not according to the National Association of Home Builders who is actively supporting programs such as the use of ENERGY STAR heaters, air conditioners and appliances, as well as its own Green Building Guidelines.  A 2008 NAHB study shows that 51 percent of homebuyers are willing to pay up to $11,000 more if energy costs are reduced by just $1,000 annually. 

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  • Good list.  I'd like to comment on Myth #1 about registers. 

    Closing registers (and bedroom doors) will change room-to-room pressures and will also reduce airflow across the heat exchanger of the furnace. This can result in higher supply temperatures, but lower efficiency (less energy savings than expected).  Because ductwork systems are often undersized, the system may already be operating at less than optimal efficiency so these additional restrictions will make things worse. Efficiency loss, pressure drives within the house and lower equipment lifespan can result. In a few cases, with adequate ducts and oversized blowers, air flow reduction may be safely reduced.

    Recommended heat rise (outlet temp minus inlet temp) for most furnaces is 30-50 degrees (max 80).  A homeowner could easily check these temps after closing some registers to see if they are within limits.

    Even better, an auditor or technician with manometer and a couple of stem thermostats can get more precise measurements and make recommendations.

  • Hi Tom, I always enjoy myth busting as it is often amazing and amusing how they grow and take root. I'd like to add a couple of my favorites which are well rooted yet need to be corrected as they are very important to our energy profession.

    1. Myth "Hot air rises (by itself)": Although we often see it moving up, it never does so under its own power. When the sun heats the asphalt in a parking lot we see the wavy distortion and the hot air moving upwards, yet as hard as it is to believe, it is the surrounding cooler air sliding under that hot air that creates the upward movement. Hot air never moves up by itself.
    2. Myth "Hot air exiting a ridge vent will pull its replacement air from the path of least resistance". This is often stated as a reason to seal off those old gable vents after installing a new ridge vent (the short circuit excuse). Let's sort this one out.
    A. The exiting hot air is being pushed out, thus it is not pulling in its replacement air.
    B. The air entering or exiting that attic is doing so based upon the inside and outside pressures. The "path of least resistance" is a red herring as it only affect the volume that will flow (a large opening has less resistance), not the direction.
    There are reasons to remove or leave those old gable vents, but the short circuit theory is not one of them. We need the roofing industry to drop this excuse and educate all as to the real concerns.

    • Duct systems are often already undersized badly enough without further flow reductions. I like zoning, but only when it is combined with two stage or variable capacity systems.

      Heat pump efficiency drops with reduced airflow, and beyond a certain point compressors are threatened by excessive head pressure and current.

      As for setbacks, they can work, but any use of aux resistance heating during recovery demolishes the relatively minor savings the would otherwise accrue.

  • Great post on the facts and myths! A good one to add to the list, there are too many factors that affect energy use. I feel a driving a change in energy consumption with a high degree of confidence.

  •  In fact, setting your temperature back 10 or more degrees for 8 hours while you sleep or go to work can reduce your energy bill by 5-15%.  

    Will this prescriptive recommendation work for everyone?  Will it cause no-one to use MORE energy?  Do you think this recommendation could potentially cause some to use more energy?  What about our charge to "do no harm"?  Could this behavior potentially create health, safety and durability issues (condensation and mold)?  

    As professionals in the field of Energy Efficiency, shouldn't we be tailoring our recommendations to fit the needs of our clients and their specific situations?  

    I really feel making prescriptive recommendations that could potentially cause harm is malpractice.  Are you sure you want your name associated with such recommendations?  Are you a thermostat salesman?   

    People want to be comfortable.  Let's stop telling them college tuition payments are found by turning back thermostats.  Broad sweeping promises of savings nobody tracks are the sleight of hand shell games we need to stay away from if we are ever to build credibility.  

    Do you see the ethical and credibility risk of such recommendations: "Why should I believe you can save me energy.  I did that thermostat thing, froze my butt off, and didn't notice any savings.  I don't believe you know how to save people energy."  

    If what we do is a profession, we need to see these houses, and really help people save energy.  Verified savings.  Or we are just going to get lumped together with all the other shysters and hucksters out there. 

    • Setbacks make a difference in most homes if combined with utility time of use or variable peak pricing energy cost structures. Setting back 5 degrees when rates are 4 times that of off peak will make a big difference in most electric bills. With more utilities implementing smartmeters keep a look out for TOU/VPP pricing, it's coming. Without TOU or VPP price plans the difference is substantially less, especially if the house is well insulated/high mass.

    • Reducing your thermostat saves energy when it's cold outside because you are reducing the difference between the inside and outside temperatures. This practice will never use more energy. Giving a range, like 5 to 15% is a reasonable thing to do; Of course the result will vary depending how deep your setbacks are - that is up to the comfort levels of the client (and the R value of the of the quilt used at night).

  • Tom,

    I completely agree with all these except the first. There is an old, but well done empirical study showing savings from closing registers by Bill Levins at Oak Ridge National Laboratory.

    Levins, W.P. 1988. “Experimental Measurements of Heating Season Energy Savings from Various Retrofit Techniques in Three Occupied Houses,” ORNL, Oak Ridge National Laboratories, Oak Ridge, TN.

    In that work, Levins did experiments on unoccupied, heavily instrumented homes in Knoxville, TN and found that closing off the registers in two bedrooms and closing the doors reduced space heating use by 20%. That's big.

    Certainly doing that will increase duct leakage and house leakage due to differential pressurization, but perhaps not more than the more than compensating savings.  However, it is a fact that registers are closed in real homes. You may not like it, but it is being done.

    While Levins showed 20% savings in the Karns houses, carefully experimental work that Iain Walker did in 2003 showed that there would be no savings from savings by closing registers in homes at any leakage level:

    I.S. Walker,  2003. "Register Closing Effects on the Performance of Central Heating Systems, LBNL- 54005, Lawrence Berkley National Laboratory, November 2003.

    It will be noted in the original publication that the detailed experimental work largely looked at impacts on duct losses and then extended the results through a simulation (REGCAP). However, it is important to note that in that work they did not actually examine overall thermal performance in a real home. It was simulated. Therein my hesitation on the issue.

    However, it is quite possible that closing off registers would save nothing in a home with considerable duct and envelope leakage. Still, the fact that the Karns research showed savings in repeated periods in a carefully done empirical study in real homes indicates to me that this issue is not resolved. Two studies coming to different conclusions.

    Future episode of Mythbusters?

    In any case, there are several investigations showing that zoning homes will save energy unless they are very well insulated (e.g. Passivhaus). This one in the PNW by PNNL showing that zoned heating systems (eg. baseboards) save energy versus central systems.

    D.S. Parker, 1989. "Thermal Performance Monitoring Results from the Residential Standards Demonstration Program," Energy and Buildings, 13, pp. 231-248.

    In this work I did while at the Northwest Power Planning Council, evaluating the a large sample of metered electrically heated homes, we found that 108 baseboard electric homes used 56.8 kWh/m2 against 71.9 kWh/m2 for 91 forced air electric ones. While the largest part of this 27% difference is certainly duct losses, I believe that some portion of this is due to zoning.

    In fact, it must be acknowledged that in most of the rest of the homes in the world, zoning is practiced: hydronic heating throughout Europe and mini-split air conditioners used for cooling just about everywhere except in North America.

    So, I think I would recast that first myth: "Zoning Doesn't Save." 

    I think it does.

    Danny Parker

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